Hematopoietic stem cell (HSC) gene therapy has been shown to result in substantial improvement and even cure for a number of diseases such as hemoglobinopathies and adrenoleukodystrophy. In addition, HSC transplantation has recently been shown to result in the cure of HIV when HIV-resistant donor cells from a donor with a rare mutation in the HIV co-receptor CCR5 were used in an allogeneic transplantation. While this study showed that transplantation of CCR5-negative cells could result in an HIV cure, finding an HLA-matched CCR5-negative donor is exceedingly rare. Thus as a surrogate approach many investigators are exploring the use of genetically modified HIV-resistant autologous cells. However, relatively high levels of genetically modified/HIV resistant cells are necessary and this can often not be achieved even after a myeloablative conditioning regimen. We have shown in a nonhuman primate model using HSCs gene-modified with a MGMTP140K mutant transgene that we can achieve efficient increases of gene-modified cells in vivo. Thus, we would like to test this strategy in a patient population that has been shown to benefit from an autologous transplantation and that may also benefit from both the anti-tumor effect of low-dose chemotherapy used for in vivo selection and from the resulting increased levels of genetically modified and HIV-resistant HSCs. We have previously shown that we can achieve low-level engraftment of gene-modified HIV-resistant cells in patients with AIDS-related lymphoma. However, engraftment of gene-modified cells was too low to result in any significant therapeutic benefit. In the current application, we propose to use a potent HIV entry inhibitor (C46) and the potent P140K selection cassette to increase the level of gene-modified HIV resistant cells in patients. The use of in vivo selection would have wide applications not only for the treatment of HIV but also genetic diseases and in particular hemoglobinopathies where high levels of gene-modified cells are necessary to alleviate all clinical manifestations of the disease. A major strength of this proposal is the collaboration between investigators from two institutions with unique expertise in the fields of gene therapy, transplantation and clinical HIV. Our overall hypothesis is that an autologous HSC transplantation with cells gene-modified with a potent anti-HIV transgene will lead to control of HIV and associated complications. Furthermore, inclusion of a potent in vivo selection transgene, P140K, will allow us to significantly increase the levels of HIV-resistant CD4 cells following transplantation. Based on extensive preclinical data from our nonhuman primate studies, we hypothesize that the levels of gene-modified, HIV-resistant HSCs and HSC-derived T cells obtained with our proposed approach will allow for an improved immune response and control or elimination of HIV and thus cure.